Voltammetric study of an FeS layer on a Hg electrode in supersaturated FeS chloride solution

2015 ◽  
Vol 12 (2) ◽  
pp. 123 ◽  
Author(s):  
D. Krznarić ◽  
I. Ciglenečki
Keyword(s):  
Electrode Surface ◽  
Natural Waters ◽  
Metal Sulfide ◽  
Electrochemical Analysis ◽  
Oxidation Products ◽  
Bulk Solution ◽  
Positive Direction ◽  
Chloro Complexes ◽  
Anoxic Waters ◽  
Surface Modified

Environmental context During the electrochemical analysis of natural waters, the Hg electrode could become the site for surface metal sulfide formation, such as FeS, which can have significant influence on the voltammetric determination of FeII. Reduction of FeII in such conditions can occur both on the bare Hg surface and on the FeS-modified Hg surface. Until recently, measurements of FeII have considered only the signal obtained from reduction on the bare Hg surface, and hence may have underdetermined the true FeII content of natural samples. Abstract Cyclic voltammetry at a Hg electrode was used for the study of an FeS layer formed on the electrode surface during scanning potential in a saturated FeS suspension containing FeS nanoparticles in chloride electrolyte. Newly presented results as a part of comprehensive study on FeS electrochemistry in model and natural samples confirm that the voltammetric peak at –1.1V, which can often be recorded in anoxic waters containing Fe and sulfide species, represents reduction of Fe2+ on the Hg electrode surface modified by the FeS layer. Fe0 deposited on such a modified Hg surface is reoxidisable, often producing two oxidation peaks situated between –0.8 and –0.6V (v. Ag/AgCl). These peaks represent two different Fe0 oxidation products, free Fe2+ and Fe2+ chloro complexes, FeCl+. By scanning the potential from –0.75V in the positive direction, an oxidation exchange peak of Hg and FeS at ~–0.45V occurs, which can be taken as a measure for FeS nanoparticles from bulk solution.

scholarly journals Adsorptive and Coagulative Removal of Trace Metals from Water Using Surface Modified Sawdust-Based Cellulose Nanocrystals

J ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 193-205
Author(s):  
Opeyemi A. Oyewo ◽  
Sam Ramaila ◽  
Lydia Mavuru ◽  
Taile Leswifi ◽  
Maurice S. Onyango
Keyword(s):  
Trace Metals ◽  
Adsorption Capacity ◽  
Cellulose Nanocrystals ◽  
Inductively Coupled Plasma ◽  
Electrostatic Interactions ◽  
Natural Waters ◽  
Maximum Adsorption Capacity ◽  
Solution Ph ◽  
Major Drawback ◽  
Surface Modified

The presence of toxic metals in surface and natural waters, even at trace levels, poses a great danger to humans and the ecosystem. Although the combination of adsorption and coagulation techniques has the potential to eradicate this problem, the use of inappropriate media remains a major drawback. This study reports on the application of NaNO2/NaHCO3 modified sawdust-based cellulose nanocrystals (MCNC) as both coagulant and adsorbent for the removal of Cu, Fe and Pb from aqueous solution. The surface modified coagulants, prepared by electrostatic interactions, were characterized using Fourier transform infrared, X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS). The amount of coagulated/adsorbed trace metals was then analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). SEM analysis revealed the patchy and distributed floccules on Fe-flocs, which was an indication of multiple mechanisms responsible for Fe removal onto MCNC. A shift in the peak position attributed to C2H192N64O16 from 2θ = 30 to 24.5° occurred in the XRD pattern of both Pb- and Cu-flocs. Different process variables, including initial metal ions concentration (10–200 mg/L), solution pH (2–10), and temperature (25–45 °C) were studied in order to investigate how they affect the reaction process. Both Cu and Pb adsorption followed the Langmuir isotherm with a maximum adsorption capacity of 111.1 and 2.82 mg/g, respectively, whereas the adsorption of Fe was suggestive of a multilayer adsorption process; however, Fe Langmuir maximum adsorption capacity was found to be 81.96 mg/g. The sequence of trace metals removal followed the order: Cu > Fe > Pb. The utilization of this product in different water matrices is an effective way to establish their robustness.

Mechanisms of Electrochemical N2 Splitting by a Molybdenum Pincer Complex

2021 ◽  
Author(s):  
Quinton Bruch ◽  
Santanu Malakar ◽  
Alan Goldman ◽  
Alexander Miller
Keyword(s):  
Electrode Surface ◽  
Redox Reactions ◽  
Catalytic Reduction ◽  
Reaction Pathways ◽  
Bulk Solution ◽  
Mechanistic Study ◽  
Pincer Ligands ◽  
Computational Studies ◽  
Pincer Complex ◽  
Bond Scission

Molybdenum complexes supported by tridentate pincer ligands are exceptional catalysts for dinitrogen fixation using chemical reductants, but little is known about their prospects for electrochemical reduction of dinitrogen. The viability of electrochemical N2 binding and splitting by a molybdenum(III) pincer complex, (pyPNP)MoBr3 (pyPNP = 2,6-bis(tBu2PCH2)-C5H3N)), is established in this work, providing a foundation for a detailed mechanistic study of electrode-driven formation of the nitride complex (pyPNP)Mo(N)Br. Electrochemical kinetic analysis, optical and vibrational spectroelectrochemical monitoring, and computational studies point to two reaction pathways: in the “reaction layer” pathway, the molybdenum(III) precursor is reduced by 2e– and generates a bimetallic molybdenum(I) Mo2(-N2) species capable of N–N bond scission. In the “bulk solution” pathway the precursor is reduced by 3e– at the electrode surface to generate molybdenum(0) species that undergo chemical redox reactions via comproportionation in the bulk solution away from the electrode surface to generate the same bimetallic molybdenum(I) species capable of N2 cleavage. The comproportionation reactions reveal the surprising intermediacy of dimolybdenum(0) complex trans,trans-[(pyPNP)Mo(N2)2](-N2) in N2 splitting pathways. The same “over-reduced” molybdenum(0) species was also found to cleave N2 upon addition of lutidinium, an acid frequently used in catalytic reduction of dinitrogen.

scholarly journals Direct electrochemical analysis of dexamethasone endocrine disruptor in raw natural waters

2012 ◽  
Vol 23 (1) ◽  
pp. 110-119 ◽  
Author(s):  
Thiago M. B. F. Oliveira ◽  
Francisco W. P. Ribeiro ◽  
Jefferson M. do Nascimento ◽  
Janete E. S. Soares ◽  
Valder N. Freire ◽  
...  
Keyword(s):  
Endocrine Disruptor ◽  
Natural Waters ◽  
Electrochemical Analysis

The development of electrochemical methods for determining nanoparticles in the environment. Part II. Chronoamperometric study of FeS in sodium chloride solutions

2014 ◽  
Vol 11 (2) ◽  
pp. 187 ◽  
Author(s):  
Elvira Bura-Nakić ◽  
Marija Marguš ◽  
Ivana Milanović ◽  
Darija Jurašin ◽  
Irena Ciglenečki
Keyword(s):  
Natural Waters ◽  
Mercury Electrode ◽  
Vital Role ◽  
Mercury Surface ◽  
Electrode Potentials ◽  
Anoxic Environments ◽  
Wide Range ◽  
Reduction Current ◽  
Surface Modified ◽  
Current Transients

Environmental contextIn anoxic environments FeS is both an important mediator in the Fe and S biogeochemical cycles and plays a vital role in controlling the scavenging and availability of many trace metals. Electrochemical detection of colloidal and particulate FeS in natural waters can be done by voltammetric measurements. The recorded anodic waves, however, are rather qualitative and lack information on the FeS concentration and size distribution. AbstractThe interactions of FeS nanoparticles (NPs) with a hanging mercury drop electrode in NaCl solutions were monitored by chronoamperometric measurements. Collisions of FeS NPs with the mercury surface were studied over a wide range of electrode potentials (between 0 and –1.9V v. Ag/AgCl). Faradaic impact transients were recorded only at the negative potentials (between –1.5 and –1.9V). It was shown that the mercury electrode surface modified with a FeS adlayer catalyses sodium reduction by shifting the potentials of this process to more positive values. This catalytic process together with possible hydrogen evolution is assumed to be the physicochemical basis for the determination of FeS NPs. Chronoamperometric measurements at the electrode potential of –1.9V showed that the reduction processes of sodium and hydrogen on FeS NPs upon collision are the main cause of sharp reduction current transients. At sufficiently positive electrode potentials (~–1.5V) the colliding FeS NPs would not be immediately repelled; instead they remained adhered to the mercury surface, causing ‘staircase-like’ chronoamperometric signals. It appears that recorded reduction current transients are carrying FeS NPs’ size information, which is consistent with parallel dynamic light scattering (DLS) measurements.

scholarly journals Electrochemical Synthesis of Polyaniline/Poly-O-Aminophenol Copolymers in Chloride Medium

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Lucia H. Mascaro ◽  
Alessandra N. Berton ◽  
Liliana Micaroni
Keyword(s):  
Cyclic Voltammetry ◽  
Conducting Polymer ◽  
Electrochemical Synthesis ◽  
Electrode Surface ◽  
Oxidation Products ◽  
Monomer Mixture ◽  
Nacl Solution ◽  
Chloride Medium ◽  
Vis Spectroscopy

The copolymerization ofo-aminophenol (OAP) and aniline (ANI) on Pt and ITO electrodes was studied using cyclic voltammetry in 0.1 M HCl/0.4 M NaCl solution. The films were characterized by SEM, cyclic voltammetry, and UV-Vis spectroscopy. The properties of the copolymer were compared with PANI and POAP films. The results strongly suggest that the growth of PANI-POAP films does not consist of the simple buildup of layers of homopolymers on the electrode surface as a result of OAP or ANI oxidation products in the monomer mixture, but that a new conducting polymer is formed by copolymerization.

Effects of aging and transformation of Fe(III)-precipitates on the retention of co-precipitated phosphate

2021 ◽  
Author(s):  
Ville Nenonen ◽  
Ralf Kaegi ◽  
Stephan J. Hug ◽  
Stefan Mangold ◽  
Jörg Göttlicher ◽  
...  
Keyword(s):  
Natural Waters ◽  
Colloidal Stability ◽  
P Uptake ◽  
Oxidation Products ◽  
Structure Stability ◽  
Retention Capacity ◽  
X Ray ◽  
P Release ◽  
P Retention ◽  
Over Time

<p>The cycling of phosphorus in terrestrial and aquatic systems is tightly coupled to the redox-cycling of iron (Fe). The oxidation of dissolved Fe(II) in natural waters leads to the precipitation of amorphous to poorly crystalline Fe(III)-solids that can bind phosphate (P) and other nutrients as well as toxic compounds. The EU project P-TRAP is aimed at developing methods to reduce diffuse P inputs into surface waters to mitigate eutrophication, by using Fe-rich byproducts from water treatment (https://h2020-p-trap.eu/). Within this project, we study mechanistic aspects of the formation and transformation of P-containing Fe(III)-precipitates and their implications for P retention in soils and water filters.</p><p>Freshly formed Fe(III)-precipitates are metastable and can transform into more stable phases over time. This may lead to the release of co-precipitated P. In laboratory experiments, we assessed how Ca, Mg, silicate (Si) and P impact on the formation and transformation of Fe oxidation products (at 0.5 mM Fe) and their P retention in synthetic bicarbonate-buffered groundwater. The time-resolved experiments were performed in electrolyte solutions containing Na, Ca, or Mg as electrolyte cation, without or with Si (at molar Si/Fe of 1), and P (P/Fe of 0.3 and 0.05). Changes in dissolved element concentrations over time were linked to changes in the structure and composition of the Fe(III)-solids; with Fe coordination probed by X-ray absorption spectroscopy, mineralogy by X-ray diffraction, and nano-scale morphology and composition heterogeneity by transmission electron microscopy with energy-dispersive X-ray detection.</p><p>The freshly-formed Fe(III)-precipitates were mixtures of amorphous Fe(III)-phosphate with either poorly-crystalline lepidocrocite (without Si) or Si-containing ferrihydrite (with Si). Increases in dissolved P during aging were largest in Na electrolytes without Ca, Mg or Si, and were linked to the transformation of amorphous Fe(III)-phosphate into lepidocrocite with a lower P retention capacity than Fe(III)-phosphate. In Ca- and to a lesser extent Mg-containing electrolytes, the Ca or Mg stabilized the amorphous Fe(III)-phosphate and thereby reduced P release over time. The presence of Si increased initial P uptake and inhibited P release during aging by causing the formation of Si-ferrihydrite with higher P sorption capacity than lepidocrocite formed in the absence of Si. In conclusion, the extents to which P is trapped by fresh Fe(III)-precipitates and released during aging can be attributed to the individual and coupled impacts of Ca, Mg and Si on Fe(III)-precipitate structure, stability and transformation.</p><p>In continuing work, we aim to expand our work to study how organic compounds impact on the formation and colloidal stability of Fe(III)-precipitates and P retention.</p>

Pure Metal Nanoparticles for Selective Electrochemical Sensor of Organic Substances

2016 ◽  
Vol 683 ◽  
pp. 288-294
Author(s):  
Anastasiia V. Shabalina ◽  
Kceniya Belova
Keyword(s):  
Ascorbic Acid ◽  
Electrode Surface ◽  
Metallic Nanoparticles ◽  
Modified Electrodes ◽  
Pure Metal ◽  
Electrochemical Analysis ◽  
Stabilizing Agents ◽  
Sensitivity And Selectivity ◽  
Electro Oxidation ◽  
Surface Increase

The field of application of electrochemical analysis has been significantly widened after modified electrodes appeared. Metallic nanoparticles are ones of the most common used modifiers of the electrode surface to increase the sensitivity and selectivity of the analysis. Increasing of selectivity is extremely important in cases when two or more analyts have electro-chemical signals at nearly the same values of electrode potential. Dopamine and ascorbic acid are an example of such case. In present work Au, Pt, Pd, and Ni “pure” nanoparticles obtained by laser ablation without stabilizing agents were used to modify the surface of a glassy carbon electrode. Modified electrodes were tested in solutions of ascorbic acid and dopamine at their simultaneous electro-oxidation. It was shown that Au, Pt, and Ni nanoparticles on the electrode surface increase the selectivity of analysis giving two separate peaks of analyts.

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